Mobile Mouse - Expensive
If you watch your computer from a distance (usually for entertainment) then this will allow you to use your iOS device as a trackpad for mouse control, and keyboard for typing. Works for windows and mac computers. It's an expensive app relative to the cost of most apps, but it's worth it if you regularly watch TV, Blu-ray/DVD, Netflix, or hulu on your computer from your couch.
Thank you for this - now I have the missing piece for setting up my HTPC.
I've never used iOS so I can't comment on the iOS ports of these apps, but I have used the Android versions of these and found them to be excellent. Given the relative ease of coding for iOS vs coding for Andriod, I can't imagine the iOS versions would be worse:
Waze - Free crowdsourced navigation, intended for commuters but I use it for long-distance navigation just fine. Shows you traffic speeds, accidents, speed traps, etc, and alerts you when you're coming up on them. You can ping other Waze users to ask about traffic further along the route, or just to chat (not recommended while driving). Yes, there's also Apple Maps, but Waze won't deposit you in the middle of Lake Erie when you're just trying to get to Bay Village (like Apple Maps threatened to do to me the one time I used it).
You Need A Budget (YNAB) - Hands down, best home budgeting software I've ever used. The desktop software is $40 but comes with free lifetime upgrades and a license to install on as many computers as you want. Once your budget is made, it can sync with the YNAB app ($5) via Dropbox so you always have access to your budget. The app lets you input and edit transactions as well. As of right now, you can't edit the actual budget from the app (at least not from Android), but I think that's coming.
Sketchbook - A basic drawing app that I use all the time for in-the-field room diagrams. Plenty of options for brushes and pencils, though, and you can save as either a flattened image or a photoshop project.